58 FRAGMENTS OF SCIENCE. 



of the jruitful soil of observation. Having started with 

 the savage, and his sensations of muscular force, we 

 pass on to the observation of force exerted between a 

 magnet and rubbed amber and the bodies which they 

 attract, rising, by an unbroken growth of ideas, to a 

 conception of the force by which sun and planets are 

 held together. 



This idea of attraction between sun and planets had 

 become familiar in the time of Newton. He set him- 

 self to examine the attraction ; and here, as elsewhere, 

 we find the speculative mind falling back for its 

 materials upon experience. It had been observed, in 

 the case of magnetic and electric bodies, that the 

 nearer they were brought together the stronger was the 

 force exerted between them ; while, by increasing the 

 distance, the force diminished until it became in- 

 sensible. Hence the inference that the assumed pull 

 between the earth and the sun would be influenced by 

 their distance asunder. Guesses had been made as to 

 the exact manner in which the force varied with the 

 distance ; but Newton supplemented the guess by the 

 severe test of experiment and calculation. Comparing 

 the pull of the earth upon a body close to its surface, 

 with its pull upon the moon, 240,000 miles away, 

 Newton rigidly established the law of variation with 

 the distance. But on his way to this result Newton 

 found room for other conceptions, some of which, 

 indeed, constituted the necessary stepping-stones to his 

 result. The one which here concerns us is, that not only 

 does the sun attract the earth, and the earth attract the 

 sun, as wholes, but every particle of the sun attracts 

 every particle of the earth, and the reverse. His con- 

 clusion was, that the attraction of the masses was simply 

 the sum of the attractions of their constituent particles. 



This result seems so obvious that you will perhaps 



